1. Technical Field
The present invention relates to a discharge lamp drive device, a projector, and a discharge lamp drive method.
2. Related Art
As shown in, for example, JP-A-2007-27145 (Document 1), there has been known a projector equipped with a resonant circuit in order to obtain a high voltage for starting discharge of the discharge lamp. In such a projector, when lighting the discharge lamp, the high voltage can be obtained by matching the frequency of the alternating-current power supplied to the discharge lamp with the resonant frequency of the resonant circuit.
Incidentally, individual difference and aging variation exist in the inductance component and the capacitance component of the resonant circuit. Therefore, if the frequency of the alternating-current power, which is supplied to the resonant circuit when lighting the discharge lamp, is fixed, there can occur the case in which the resonance fails to occur, and as a result, the discharge lamp fails to light. In order to avoid such a problem, according to the technology disclosed in Document 1, the frequency of the alternating-current power supplied to the discharge lamp is increased monotonically toward the resonant frequency to thereby find out the actual resonant frequency in every lighting operation.
However, in this method, in the period until the discharge lamp starts lighting, there continues the state in which the frequency of the alternating-current power is approximate to the resonant frequency. Therefore, the voltage and the current in the resonant circuit increase, and the heat generation in the resonant circuit increases. Thus, there is a possibility that elements of the drive device of the discharge lamp are damaged.
To deal with the problem described above, it is possible to adopt a method of providing a period, in which the frequency of the alternating-current power is set to a value substantially different from the resonant frequency, to thereby decrease the voltage and the current in the resonant circuit. However, if the voltage in the resonant circuit is too low, in the case in which the discharge lamp is put off in the period of setting the frequency of the alternating-current power to the value substantially different from the resonant frequency, it is difficult for the discharge lamp to relight. Therefore, there is a problem that the lighting performance of the discharge lamp degrades.